How long is the human small intestine?

In many people's impressions, the small intestine mainly plays the role of absorbing nutrients. In fact, the function of the human small intestine is very powerful. In addition to its absorption ability, it also has the function of secretion. It is reported that the human small intestine will secrete small intestinal fluid, which includes a variety of enzymes, so it is very helpful for the digestion of food. So what is the approximate length of a normal person's small intestine?

How long is the human small intestine?

The small intestine is located in the abdomen. The upper end is connected to the pylorus and the stomach, and the lower end is connected to the large intestine through the pylorus. It is the main place for food digestion and absorption. The small intestine is coiled in the abdominal cavity, connected to the pylorus of the stomach above and the cecum below. It is about 4-6 meters long and is divided into three parts: the duodenum, jejunum and ileum. Digestion in the small intestine is crucial because the digestion process is basically completed after the food is chemically digested by pancreatic juice, bile and small intestinal fluid in the small intestine and mechanically digested by small intestinal movement, and the nutrients are absorbed by the small intestinal mucosa.

The small intestine is generally divided into three sections based on its morphology and structure, namely the duodenum, jejunum and ileum.

The duodenum is located in the posterior and superior part of the abdominal cavity and is 25 cm long. Its upper part (also called the bulb) is connected to the pylorus of the stomach and is a high-risk site for ulcers. The bile secreted by the liver and the pancreatic juice secreted by the pancreas are excreted into the duodenum through the openings of the common bile duct and the pancreatic duct on the duodenum to digest food. The duodenum is in the shape of a "C", wrapping around the head of the pancreas from the right side, and can be divided into four parts: the upper part, the descending part, the horizontal part, and the ascending part.

1. The superior part starts from the pylorus of the stomach on the right side of the first lumbar vertebra, goes to the right and rear, and then turns sharply downward below the liver hilum to become the descending part of the duodenum. The 2.5 cm section of intestine that connects to the pylorus at the top has a thin wall, smooth mucosa without annular folds, and is also called the duodenal ampulla (bulb), which is a high-incidence site for duodenal ulcers.

2. The descending part descends along the right side of the 1st to 3rd lumbar vertebrae, turns left at the plane of the 3rd lumbar vertebra, and becomes the horizontal part. There is a longitudinal mucosal fold on the posteromedial wall of the descending part, called the longitudinal fold of duodenum, with the major duodenal papilla at its lower end, which is the common opening of the common bile duct and pancreatic duct. It is about 75 cm away from the central incisor and can be used as a reference for the depth of insertion of the duodenal drainage tube.

3. The horizontal part (horizontal part) crosses the inferior vena cava and the front of the third lumbar vertebra from right to left at the third lumbar vertebral plane, and transforms into the ascending part in front of the abdominal aorta. The superior mesenteric artery and vein cross the front of the horizontal part.

4. The ascending part rises obliquely from the horizontal part to the upper left to the left side of the second lumbar vertebra, turns forward and downward to continue with the jejunum. The bend formed by this turning part is called the duodenojejunal flexure.

The posterior superior wall of the duodenal flexure is fixed to the posterior abdominal wall by the suspensory muscle of duodenum. The duodenal suspensory muscle is composed of muscle fibers and connective tissue, covered with peritoneum on the surface. It is clinically called the Treitz ligament and is an important landmark for confirming the beginning of the jejunum during surgery.

The jejunum connects to the duodenum, accounts for 2/5 of the total length of the small intestine, and is located in the upper left part of the abdominal cavity. The ileum is located in the right lower abdomen and accounts for 3/5 of the total length of the small intestine. There is no clear dividing line between the jejunum and ileum.